Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a gamma reference voltage supply pattern for driving a liquid crystal display device, and a method for driving the same.
Discussion of the Related Art
A liquid crystal display device displays an image by adjusting light transmittance of liquid crystal cells depending on a video signal. A liquid crystal display device of an active matrix type in which a switching element is formed for every liquid crystal cell is well suited for the display of a moving images using active control of the switching element. A thin film transistor (referred to hereinafter as a “TFT”) is commonly used as the switching element of an active matrix type liquid crystal display as shown in FIG. 1.
Referring to FIG. 1, the liquid crystal display device of the active matrix type converts digital input data into an analog data voltage based on a gamma reference voltage and supplies the analog data voltage to a data line DL, and, at the same time, supplies a scan pulse to a gate line GL, so as to charge a liquid crystal cell Clc.
The TFT has a gate electrode connected to the gate line GL, a source electrode connected to the data line DL, and a drain electrode connected to a pixel electrode of the liquid crystal cell Clc and one electrode of a storage capacitor Cst.
A common voltage Vcom is supplied to a common electrode of the liquid crystal cell Clc.
When the TFT is turned on, the storage capacitor Cst is charged with a data voltage applied from the data line DL. The storage capacitor Cst acts to maintain a voltage in the liquid crystal cell Clc constant.
At the time that the scan pulse is applied to the gate line GL, the TFT is turned on to form a channel between the source electrode and the drain electrode to supply the voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc. The arrangement of liquid crystal molecules of the liquid crystal cell Clc is changed due to an electric field between the pixel electrode and the common electrode, thereby modulating incident light.
A liquid crystal display device according to the related art with pixels each having this equivalent circuit includes a data driving circuit for converting input digital data into an analog data voltage and supplying the analog data voltage to a liquid crystal display panel. This data driving circuit is made up of a plurality of data drive chips as shown in FIG. 2.
Referring to FIG. 2, the data driving circuit 100 included in the related art liquid crystal display device, includes a plurality of data drive chips 110-1 to 110-i each for adjusting the level of a positive data voltage based on a positive gamma reference voltage PGMA input thereto and for adjusting the level of a negative data voltage based on a negative gamma reference voltage NGMA input thereto. Here, i is a natural number greater than or equal to 2.
The data drive chip 110-1 converts input digital data into an analog data voltage and supplies the analog data voltage to the liquid crystal display panel. The data drive chip 110-1 adjusts the level of a positive data voltage based on a positive gamma reference voltage PGMA 1 input thereto and adjusts the level of a negative data voltage based on a negative gamma reference voltage NGMA1 input thereto. Here, the positive gamma reference voltage PGMA1 and the negative gamma reference voltage NGMA1 have the same levels, and current of a level proportional to the levels of the positive gamma reference voltage PGMA1 and negative gamma reference voltage NGMA1 is supplied to the data drive chip 110-1.
The data drive chip 110-2 converts input digital data into an analog data voltage and supplies the analog data voltage to the liquid crystal display panel. The data drive chip 110-2 adjusts the level of a positive data voltage based on a positive gamma reference voltage PGMA2 input thereto and adjusts the level of a negative data voltage based on a negative gamma reference voltage NGMA2 input thereto. Here, the positive gamma reference voltage PGMA2 and the negative gamma reference voltage NGMA2 have the same levels, and current of a level proportional to the levels of the positive gamma reference voltage PGMA2 and negative gamma reference voltage NGMA2 is supplied to the data drive chip 110-2.
The data drive chip 110-(i-1) converts input digital data into an analog data voltage and supplies the analog data voltage to the liquid crystal display panel. The data drive chip 110-(i-1) adjusts the level of a positive data voltage based on a positive gamma reference voltage PGMA(i-1) input thereto and adjusts the level of a negative data voltage based on a negative gamma reference voltage NGMA(i-1) input thereto. Here, the positive gamma reference voltage PGMA(i-1) and the negative gamma reference voltage NGMA(i-1) have the same levels, and current of a level proportional to the levels of the positive gamma reference voltage PGMA(i-1) and negative gamma reference voltage NGMA(i-1) is supplied to the data drive chip 110-(i-1).
The data drive chip 110-i converts input digital data into an analog data voltage and supplies the analog data voltage to the liquid crystal display panel. The data drive chip 110-i adjusts the level of a positive data voltage based on a positive gamma reference voltage PGMAi input thereto and adjusts the level of a negative data voltage based on a negative gamma reference voltage NGMAi input thereto. Here, the positive gamma reference voltage PGMAi and the negative gamma reference voltage NGMAi have the same levels, and current of a level proportional to the levels of the positive gamma reference voltage PGMAi and negative gamma reference voltage NGMAi is supplied to the data drive chip 110-i.
Further, the data drive chips 110-3 to 110-(i-2) have the same functions as those of the above-stated data drive chips 110-1, 110-2, 110-(i-1) and 110-i.
Notably, the positive gamma reference voltages PGMA1 to PGMAi have different levels and the negative gamma reference voltages NGMA1 to NGMAi also have different levels. As a result, currents of different levels are supplied to the data drive chips 110-1 to 110-i.
For example, assuming that the positive gamma reference voltage PGMA1 and negative gamma reference voltage NGMA1 are lowest in level and the positive gamma reference voltage PGMAi and negative gamma reference voltage NGMAi are highest in level, current of a very high level is supplied to the data drive chip 110-i, whereas current of a relatively low level is supplied to the data drive chip 110-1. As a result, excessive heat is generated in the data drive chip 110-i due to the supplied current of the high level.
As mentioned above, the related art liquid crystal display device has a disadvantage in that excessive heat is generated in data drive chips supplied with currents of high levels, among a plurality of data drive chips. Moreover, because a positive gamma reference voltage and a negative gamma reference voltage having the same levels are supplied to each data drive chip, the addition of current supplied together with the positive gamma reference voltage and current supplied together with the negative gamma reference voltage may excessively raise the temperature of data drive chips due to the heat being generated in specific data drive chips.